Analysis and prediction of uniaxial compressive strength of icy lunar regolith under extreme temperature

Abstract

Water ice exists in the permanently shadowed region (PSR) of the moon. It can become a vital survival material for the lunar base and provide fuel for the moon to make the moon a relay station for deep space exploration. For in-situ sampling and detection of lunar water ice, the design of sampling equipment has to consider the mechanical properties of the icy lunar regolith (ILR) to be broken during the drilling process. According to the mineral and chemical composition of the soil in the PSR, basalt rocks and anorthosite rocks are selected as two basic raw materials to simulate lunar soil. Multiple sets of ILR simulated samples are prepared with different raw material ratios (five kinds), water content (5–25 wt%), dry density (bulk density, excluding water, 1.45–1.97 g/cm3), and temperature (−240 to −10 °C). Uniaxial compressive strength (UCS) tests are carried out on these samples. A comprehensive mapping model between the UCS and the above four factors is constructed using multiple nonlinear regression methods. Based on the existing remote sensing data, the relationships or hypotheses of the subsurface dry density, temperature, and water content with depth are given. Furthermore, the UCS and drillability grade of ILR are predicted to change with depth. The results show that the ratio of raw materials has far less influence on the UCS than the other three factors. When the sample temperature is lower than −180 °C, the degree of influence of temperature changes on the UCS is significantly reduced. The UCS of the sample increases nonlinearly with the increase of dry density. The samples have an extreme strength value in the saturated water content state. This study provides a standard for the design of the equipment for drilling detection of water ice and lays a foundation for presetting operating procedures of the drilling tool.